1. Field of the Invention
This invention relates to a molded synthetic resin surface fastener in which a substrate sheet and a multiplicity of engaging elements projecting from one surface of the substrate sheet are formed integrally with each other, and more particularly to a molded surface fastener which has adequate engaging strength and rate suitable for use in a joint of industrial materials, such as ceiling materials and wall materials which are subject to peeling forces and which has adequate durability without giving damage to engaging elements of the companion surface fastener during peeling.
2. Description of the Related Art
Molded surface fasteners of the described type have greater engaging strength compared to the ordinary knitted or woven surface fasteners and are therefore widely used in joining interior ornamental materials, such as wall materials and ceiling materials. Generally, the individual engaging element of the molded surface fastener has a stem standing from one surface of a substrate sheet, and a hook curving in one direction from the distal end of the stem and terminating in an end directed to the surface of the substrate sheet.
In the case that the individual engaging element of the molded surface fastener is a hooked member having the above-mentioned simple hook structure, in order to increase the degree of strength of engagement with a looped member, which is the companion engaging element, it has been customary to mold the engaging elements of rigid synthetic resin or to increase the thickness of the looped member. However, the rigid engaging element will give an undesirable touch, and it tends to be out of engagement of the companion looped member. In the case of the thick looped member, the surface fastener not only would become rigid but also would have less engaging elements per unit area on the substrate sheet, thus making it difficult to secure a predetermined degree of engaging strength.
Consequently, soft synthetic resin materials, such as polyester, polyamide and polyurethane, usually suitable for molded surface fasteners are used, and at the same time, various forms of engaging elements are put into practice in order to secure the relative strength of hooked and looped members and in order to increase the engaging strength. A typical form of engaging element, as disclosed in, for example, Japanese Patent Laid-Open Publications Nos. SHO 47-31740 and HEI 4-224703, has front and rear engaging portions symmetrically projecting from the distal end of a generally trapezoidal hook. An alternative form, as disclosed in, for example, Japanese Utility Model Laid-Open Publication No. HEI 4-128611, has the distal end of a stem being branched and one of the branched end is made to have a hook shape. According to these known forms, the number of engaging elements per unit area on the substrate sheet increases to increase the rate of engagement with companion engaging elements so that the engaging strength of the entire surface fastener is increased.
In the molded surface fastener to be used in the industrial materials, a predetermined space must be provided between each adjacent pair of engaging elements due to the mold technology. Consequently the density of engaging elements on the substrate sheet surface is necessarily limited to a considerably low degree compared to the density of looped members of the companion surface fastener. Even if an attempt is made to increase the rate of engagement by providing each engaging element with hooks facing in opposite directions as disclosed in the above-mentioned publications, the rate of engagement has a limit as the number of looped members actually engaged with the engaging elements of the molded surface fastener is several tens percent of the total number of looped members.
In an attempt to increase the rate of engagement of hooks with looped members entering between front and rear engaging elements adjacent to each other in the same rows, the engaging element disclosed in, for example, European Pat. No. 0464753A1 has a rear rising surface in a position on the substrate sheet surface at which position a perpendicular line passing through the end of the hook of the rear next engaging element meets the substrate sheet surface. According to this arrangement, if the looped member is raised along the rear surface of the front next engaging element, there is no guarantee that the looped member may come into engagement with the hook of the rear next engaging element. Further, with this type conventional molded surface fastener, most of the looped members entered between every adjacent pair of rows of hooks remain unengaged with the hooks.